This invention relates to a process for the reaction of water moistened particulate metal chlorides, sulfates or oxides with nitrogen dioxide gas in a fluidized state, with the production of a solid having a composition composed of the metal and the nitrate ion. More particularly, the invention relates to the production of potassium nitrate or calcium nitrate and nitrosyl chloride gas (depending on the composition of the particulate) using nitrogen dioxide gas and water moistened particulate potassium chloride or calcium sulfate in an energy efficient process using counter current flow and fluidized bed technology. The unique aspects of this process is that it permits the reaction to take place at a rapid rate at moderately elevated temperatures while retaining essentially the same crystal size as the original potassium chloride or calcium sulfate. The counter current aspects of the invention permit the production of potassium nitrate or calcium nitrate and nitrosyl chloride gas (depending on the solid) essentially free of nitrogen dioxide.
Potassium is one of three essential elements (N.P.K.) in the life cycle of all plants. Fertilizers therefore generally contain all three in one form or another. Potassium, however is generally present as a chloride since it is the most readily available, least expensive potassium compound. For many crops (e.g., citrus, tobacco) a fertilizer containing small amounts of chlorides is toxic. Thus, there is created a sizable demand for manufactured potassium nitrate as a non-chloride source of potassium. However, it must be produced at a relatively low cost to compete with existing processes such as that produced from natural deposits. The use of potassium nitrate as a fertilizer was first suggested by Glauber in 1655. A few years later its value was discussed by Digby in what is said to be the earliest known record of the actual use of fertilizers as distinct from decaying organic matter. The world supply of potassium nitrate was formerly derived from incrustations on the soils around habitations in tropical countries, chiefly India, Sri Lanka, Mexico and Egypt. Its presence there is due to the decomposition of organic matter by nitrifying organisms in soils containing soluble potassium compounds.
Much of the potassium nitrate in commerce was formerly made by the xe2x80x9cConversion Processxe2x80x9d in which sodium nitrate and potassium chloride undergo a double decomposition. This process depends on the wide variation in the solubility of potassium nitrate in hot and cold solutions.
KCl+NaNO3àKNO3+NaCl
This process has been displaced by more efficient operations as will be shown as follows:
Potassium nitrate, otherwise known as saltpeter or nitrate of potash, is important in the production of fertilizers, explosives, glass, and numerous other industrial chemicals. It is one of the oldest known xe2x80x9cindustrialxe2x80x9d chemicals. Potassium nitrate has been used on a large scale since around the year 1300, when the Chinese discovered that saltpeter could be combined with sulfur and charcoal to produce the common explosive known as black powder. The ever-growing demand for potassium nitrate for these and other such uses has resulted in a prolonged search for improved potassium nitrate production processes, and various methods have been invented to produce potassium nitrate. For example, large quantities of potassium nitrate are commercially produced by the reaction of potassium chloride with nitric acid in the presence of oxygen, yielding the following overall reaction:
2KCl+2HNO3+1/2O2xe2x86x92KNO3+Cl2+H2O
The potassium chloride and nitric acid must be reacted at 100xc2x0 C. to produce potassium nitrate, nitrosyl chloride and water as follows:
3KCL+4HNO3xe2x86x923KNO3+NOCl+Cl2+2H2O
The nitrosyl chloride is then oxidized to chlorine and nitrogen dioxide, N02, with nitric acid. See Chemical Process Industries, 4th Ed., Shreve and Brink, McGraw-Hill, Inc., New York (1977), pp. 272-273.
Smith et al, in U.S. Pat. No. 2,963,345, disclose a process for producing potassium nitrate, which involves agitating solid particulate potassium chloride with liquid nitrogen peroxide under anhydrous conditions at a temperature of 15xc2x0 C.; excess nitrosyl chloride vapors produced by the reaction are continuously withdrawn to maintain the reaction. Potassium nitrate and unreacted potassium chloride are then separated by addition to a brine that contains dissolved potassium nitrate and potassium chloride; the brine solution is heated to about 85xc2x0 C. to dissolve the potassium nitrate, but not the solid particles of potassium chloride. The solid particles of potassium chloride are then separated by filtration. Large volumes of potassium nitrate are also produced by the reaction of sodium nitrate with potassium chloride, the overall reaction being:
KCl+NaNO3xe2x86x92KNO3+NaCl
This process requires that potassium chloride be dissolved in a hot solution of sodium nitrate; upon heating, sodium chloride crystals are formed. The hot potassium nitrate solution is then run through the sodium chloride crystals forming at the bottom of the reaction vessel. However, a mixture of potassium nitrate and sodium chloride is formed, so additional processing operations are required to separate potassium nitrate.
Lehto, in U.S. Pat. No. 3,983,222, discloses a continuous process for producing potassium nitrate, which includes the steps of extracting nitrate from aqueous solutions with an organic amine salt dissolved in an organic solvent, separating the organic phase containing the extracted nitrate from the aqueous phase, and stripping the organic base with a potassium salt stripping solution having a pH of at least 0.5. The stripping solution also contains nitrate ions and potassium ions with the concentration of potassium nitrate maintained high enough to induce crystallization of potassium nitrate from the stripping solution continuously.
Dotson et al, U.S. Pat. No. 4,465,568, uses an electrolytic process to produce chloride free mixtures of sodium nitrate and potassium nitrate.
Baniel et al. discloses in U.S. Pat. No. 2,902,341 a process for the preparation of water soluble metal sulfates, phosphates, or nitrates by the reaction in aqueous medium of the chlorides of the respective metals with free sulfuric phosphoric or nitric acid, respectively. Hydrochloric acid is extracted from the aqueous liquid with a solvent of limited mutual miscibility with water but being a solvent for hydrochloric acid but not for any of the metal salts. While this process has been exploited commercially, it lacks the simplicity and efficiency of the instant method. Large volumes of liquids must be handled; crystallization, extraction, separation, and distillation processes are required to recover the desired salts and solvents. Volatile organic solvents are utilized in the extraction process requiring stringent environmental and safety standards. The major plant utilizing this process has suffered serious fires, disrupting production for significant periods of time.
Bianchi et al discloses in U.S. Pat. No. 4,776,930 a process for the production of potassium nitrate by reacting a solution of potassium carbonate with nitric acid. This process utilizes expensive raw materials (potassium carbonate produced by electrolytic process) and requires substantial energy to recover the potassium nitrate from the solution.
Abidaud et al discloses in U.S. Pat. No. 5,110,578 a process for potassium nitrate via ion exchange on a continuous basis using relatively weak solutions of nitric acid and potassium chloride. High purity solid potassium nitrate is produced by crystallization. Significant energy is required to produce solid potassium nitrate by this process due to the dilute solutions produced (15% wt KNO3 and 0.5% wt KNO3) which must be neutralized by potassium hydroxide (KOH).
Manour et al discloses in U.S. Pat. No. 4,378,342 a method of producing potassium nitrate by reacting potassium chloride with nitric acid in an organic solvent. The resulting potassium chloride is separated from the solution which contains hydrochloric acid, nitric acid and the solvents which are washed and recovered. The remaining aqueous solution of hydrochloric acid contains some nitric acid which is recovered by solvent extraction producing a substantially nitrate free hydrochloric acid. Both the nitric acid and solvent are separated and returned to the process. This process is a refinement of Baniel et al and is thought to be practiced by Haife Chemical in Israel. The plant is quite large producing in excess of 300,000 tons of potassium nitrate per year. Nonetheless the process is very capital intensive employing many unit processes including distillation, centrifrigation, refrigeration, and several different trains of extraction. It is also somewhat hazardous having had serious fires in its solvent recovery units. It is also a labor and energy intensive operation due to the complexity of the process and the energy required for refrigeration, distillation, and drying operations.
A commercial process developed in the late 1960s for the Potash Division of American Metal Climax at Vicksburg, Miss. and still in existence under different ownership, reacts potassium chloride with 65% nitric acid and recycled strong 81% nitric acid to produce a nitric acid solution containing potassium nitrate which is recovered by vacuum crystallization, drying, melting and prilling operations. Complex acid and nitrogen dioxide recovery systems are required and low temperature fractionization to recover chlorine from reaction gases. This is an extremely capital intensive process. It is also labor and energy intensive because of the complexity of the operation and the significant number of unit operations required. All of the prior art processes for producing potassium nitrate are expensive or difficult to perform.
Processes that utilize nitric acid at elevated temperatures require specially constructed equipment to handle the highly corrosive reactants, and further, elevated reaction temperatures require high-energy inputs. Other prior art processes suffer from low yields of potassium nitrate or an impure product. Thus, there is a need for an inexpensive and continuous process for producing large quantities of potassium nitrate at ambient temperatures. All of the processes outlined in the prior discussion lack the relative simplicity, energy, and operating efficiency of the instant invention from which the finished product retains essentially the same size distribution and purity of the original solid feeds. The reaction proceeds rapidly and to completion. No external heat source is required and the process is continuous with halides or sulfates being fed in the top bed and nitrates extracted from the bottom; fluidization and gravity providing the means by which the product flows from bed to bed while counter current flow of gas and or air (the fluidizing medium) permits the strongest nitrogen dioxide gas stream to contact the most nearly converted feed while the most dilute gas contacts the raw feed thus minimizing contamination of the effluent nitrosyl chloride/ chlorine gas with nitrogen dioxide or nitric oxide gas.
The primary object of this invention is to eliminate the problems and inefficiencies of the prior art by providing a new process by which metal halides and or sulfates may be reacted with nitrogen dioxide to produce solid compounds containing nitrate anion while liberating a gaseous compound containing the metal alkali cation.
A further object of this invention is to provide a new highly energy efficient process for said reactions.
A further object of this invention is to provide a new simple and cost effective process for the manufacture of said compounds.
A further object of this invention is to provide the conditions whereby the new method may be effectively performed to produce the said reactions.
A further object of this invention is to provide a granular product which may be readily blended with existing products or may be further granulated to permit coating with a slow release coating.
A further object of the invention is to provide a cost effective method to produce a high quality potassium nitrate and/or calcium nitrate.
A further object of the invention is to provide a method to convert gypsum waste from phosphate operations to a useful fertilizer, while producing sulfur dioxide or sulfuric acid for recycle to the operation.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.